Electron discharge device



Filed June 25, 1935 [Ewe J'MM INVENTOR ssesssesssssssoss a Q Q a 6 Q 0 Q Q a Q a a a a a s a o o a seasons: :3

a a a 9 scene .eoaeomaeuaoaooewnaoc oes: ssnsossoawo 0. woaoaoeeooo o .QQQSQQQQGSQSQQQQQ Patented Aug. 17, 1937 UNITED STATES PATENT CEHQE ELECTRON DISCHARGE DEVICE Application June 25,

Claims.

This invention relates to multi-grid electron discharge tubes and with particularity to tubes having a plurality of sets of elements arranged to perform different functions.

A principal object of the invention is to provide an improved form of modulating or frequency converting tube, such for example as is employed in present day superheterodyne radio receivers.

A feature of the invention relates to a fre- 10 quency converting or modulating tube of the plural grid type having a plurality of grids with varying pitch or mesh.

Another feature relates to a frequency converting or modulating tube having an oscillator section and a modulator or converting section and so designed as to have a minimum of interelectrode capacitance between the oscillator anode and the modulator grid.

A further feature relates to a frequency converting or modulating tube having an oscillator section and a modulator section with a modulator grid having sections of different pitch or mesh and with the oscillator anode arranged to be in registry with only the low mu section of the modulator grid.

A further feature is to provide a highly stable and efficient tube of the so-called pentagrid converter type wherein there is a minimum tendency to frequency drift.

A still further feature relates to the novel organization, arrangement and relative location of parts which go to make up an efficient and stable frequency converting or modulating type.

In the drawing,

Fig. l is a partial sectional view of a tube embodying features of the invention.

Fig. 2 is a diagrammatic representation of the tube of Fig. 1 showing it connected in a typical circuit.

While the invention will be disclosed as embodied in one specific type of tube which is commonly known in the art as a pentagrid converter tube, it will be understood that this is done merely for explanatory purposes and not by way of limitation. Accordingly in Fig. 1 the numeral I represents in dotted outline any well known type of enclosing envelope provided at its lower end with a reentrant stem 2 terminating in a press 3, and at its upper end in a 5 substantially cylindrical dome portion 4. Sealed into the press 3 in any well known manner are the electrode lead-in and support wires 5 to H i inclusive. Attached to the wires l0 and II are the ends of the cathode heater or filament which 55 is insulatingly mounted within the metal cath- 1935, Serial No. 28,277

ode sleeve H! which is provided on its outer surface with a suitable thermionically emissive coating 20.

Surrounding the cathode and substantially coextensive longitudinally therewith are four grid electrodes 2|, 22, 23 and 24 each of which may be of any well known fo-raminous structure such as a helically wound wire or of wire mesh. Preferably as shown, each grid is comprised of a pair of parallel metal uprights or side-rods around which is helically wound the corresponding grid wire the turns being conductively anchored to the side rods in any known manner. Thus grid 2! is wound around and has each turn conductively fastened to the side-rods 25, 26; grid 22 to side-rods 21, 28; grid 23 to side-- rods 2'3, 30; grid 24 to side-rods 3|, 32. For the purpose of accurately spacing the cathode and the various grids from one another there may be provided upper and lower spacer discs 33 and 34 respectively. These discs may be of any suit able insulating material such as mica and are provided with aligned sets of perforations to receive the ends of the grid side-rods and the ends of the cathode. The spacers may be held in place by suitable projections or lugs on the siderods and if desired the cathode sleeve may be held in place by a circumferential bead as disclosed in U. S. Patent No. 1,974,916. Surrounding all the grids is a tubular plate or anode 35 which is supported on the wires 5 and ll. Supported on the wires 8 and 13 adjacent the lower end of the cathode is an additional grid 38 which is situated between the grids 2i and 22. In accordance with the invention the lower sections of grids 2| and 22 which cooperate with the shortened grid 35, are of finer mesh or pitch than the upper sections. Thus the upper sections of grids 2| and 22 may be of relatively coarse mesh or pitch, while the lower sections of these grids may be of relatively fine mesh or pitch. On the other hand the grid 23 has its lower section of coarser mesh or pitch than its upper section as shown in Fig. 2 of the drawing wherein for the sake of clarity the various grid side-rods are omitted. The outermost grid 24 is preferably of uniform pitch as illustrated.

When the tube described is to be used as an oscillator-detector, an oscillator-modulator, or a frequency converter preferably the cathode cooperates with the lower section of grid 2| and with the grid 36 to generate local oscillations whereby the potential of grid 2! varies in accordance with these generated oscillations. The grid 23 may act as the signal control or modulating grid whereby the electron stream between the cathode and the main anode 35 is modulated. The grid 23 is electrostatically shielded from the anode 35 by means of the inner and outer shield grids 22 and 24.

A typical circuit arrangement for using the tube as an oscillator-modulator is shown in Fig. 2 wherein the numeral 3? represents schematically a suitable input transformer for impressing the incoming high-frequency carrier waves across the control or modulating grid 23 and the cathode 23, preferably through a suitable grid biasing resistor 38 or the like. Connected between the grid 2| and the cathode 26 is a feed-back coil 39 which is inductively coupled to a similar coil the latter being connected between the oscillator anode-grid 36 and a suitable positive terminal 4| of the main D. C. supply. A tuning condenser 42 may be provided to adjust the frequency of the locally generated oscillations. grids 22 and 24 are connected together by the jumper 43, and thence through a resistor to a suitable positive terminal 45 of the main D. C. supply, while the main or output anode 35 is connected through a suitable tuned output circuit to a positive terminal 46 of the main supply. The manner of functioning of the tube and circuit described is substantially as follows. The local oscillations of intermediate frequency generated by the electrodes 20, 2| and 36 cause the potential of grid 25 to vary accordingly and consequently the main electron stream between cathode 20 and anode 35 likewise varies. modulated high frequency carrier wave being impressed on control grid 23 causes this main electron stream to be correspondingly varied, resulting in the production in the anode tuned circuit of a wave of intermediate frequency bearing modulations similar to those of the received carrier impressed on grid 23. I have found that with the ordinary form of pentagrid converter tube the potential variations of the signal or control grid 23 tend to affect the potential of the oscillator anode corresponding to anode-grid 36. By

" positioning the anode-grid 36 as shown in the drawing and by making the pitch of the lower section of the inner shield grid 22 finer, I have found it possible to reduce to a minimum the tendency of the main anode and/or control grid voltage variations to affect the potential of the oscillator anode. This reduction of cross-modulation is effected not only by the mounting of the oscillator anode in the particular position shown, but also by reason of the increased shielding effect of the inner grid 22 which at its lower section is of finer pitch than the section in the main electron stream. At the same time the efficiency of the oscillator section of the tube is increased by reason of the fact that the lower section of grid 2| has its pitch also made finer. With the above described arrangement it is possible therefore to design the tube for the optimum translation transconductance in the upper or modulating section while reducing to a minimum the interelectrode capacitance between. the control grid and the oscillator anode. Various changes and modifications may be made herein without departing from the spirit and scope of the invention. Thus the oscillator anode 36 instead of being in the form of a foraminous member may be in the form of a tubular plate similar to the plate 35. Furthermore, while Fig. 2 shows the tube connected in one specific type of circuit, it will be understood that this circuit is merely representative of a number of applications of the tube as The inner and outer shield The incoming signal will be apparent to those skilled in the art. The expression pentagrid converter as employed in this specification and in the claims is intended to cover the type of tube commercially known as a pentagrid converter tube and. including a main electron emitting cathode and a main anode With five electrodes situated between the cathode and the anode. One of said electrodes serves as a virtual cathode and another electrode serves as a main modulating or control grid for the purpose of converting a carrier wave of one frequency to a corresponding carrier wave of a different frequency.

What is claimed is:

1. An electron discharge device having an electron emitting cathode, an anode, a pair of grids between said cathode and anode and substantially co-extensive in length with the oathode, another grid between said pair of grids but extending only partly along said cathode said other grid arranged ,to serve as an oscillator anode for a portion of said cathode.

2. An electron discharge device .having an electron emitting cathode, an anode,'a pair of grids between said cathode and anode and substantially co-extensive in'length with. said cathode, and another grid between said pair of grids but extending only partly along said cathode, at least one ofsaid pair of grids having a portion whichis co-extensivewith said other grid said portion being of differentimpedance fromthe remainder thereof said other grid arranged to serve as an oscillator anode with a portion of said cathode.

3. An electron discharge device having an of said pair of grids adjacent said other grid being of different impedance from the remaining portions of said pair of grids.

4. An electron discharge device comprising an electron emitting cathode, 3.11;3110d6, a-member serving as an oscillator grid to said cathode, an

electrode serving. as an oscillator anode to said cathode, said electrode being. situated adjacent one section only of the oscillator grid, a shield grid substantially co-extensive with said oscillator grid, a modulator grid the section of the electron emitting cathode, an anode, four gridsv between said cathode and anode and substantially co-eXtensive-in length with said cathode, a

grids, at least two of said four grids having different pitches at their end portions adjacentsaid fifth electrode.

6. An electron discharge device of the pentagrid convertertype in which the control grid has a portion of low mu and a portion of high mu, and a shield grid having a portion of high mu and a portion of low mu, the oscillator anode being situated adjacent only the low mu portion of the control grid and the highmu portion of the shield grid.

7. A pentagrid converter tube having an electron emitting cathode, a first grid substantially co-extensive in length with said cathode and .160 fifth electrode between the first and second having one portion arranged to act as a virtual cathode and another portion arranged to act as an oscillator grid, 2. control grid substantially co-extensive in length with the first grid, and an oscillator anode situated adjacent only the oscillator section of the first grid.

8. A tube according to claim '7 in which the control grid has a portion of low mu where it is adjacent said oscillator anode.

9. A tube according to claim 7 in which a shield grid is positioned between the control grid and the oscillator anode, said shield grid having a high mu portion adjacent said oscillator anode.

10. An electron discharge device of the pentagrid converter type having an electron emitting cathode, a first grid arranged to act as a virtual cathode and as an oscillator grid, an oscillator anode situated adjacent one section only of said first grid, a control grid substantially co-extensive with the first grid and having portions of difierent mu the portion of low mu being situated adjacent said oscillator anode, a shield grid between said oscillator anode and said control grid said shield grid having portions of difierent mu 10 

